Heatsinks and ULA chips.

[Nick]

Nothing reduces the life of electronics kit more than heat and high voltages.

My absolute favourite oscilloscopes, the Tektronix 2465 series, use a hybrid vertical amplifier that is made from unobtainium, know as "U800" (the number it always seems to have on schematics) or more properly "155-0241-02" !

Certain batches of them were prone to over-heating and thus rendering the scope junk - some guys have designed SMT replacements but they are complex, e.g. http://www.davmar.org/TE/Tek2465/lafay.html

Touch wood, my 2465B, considered by many to be the best analogue 'scope ever made, is still going strong after some minor repairs...